1. Technical Field
The present invention relates to a piezoelectric oscillator and a transmitter equipped with the piezoelectric oscillator.
2. Related Art
In recent years, in order for coping with increase in communication speed associated with rapid development in the information-communication technology and the network technology, oscillators used for communication devices are required to be high-frequency devices and to have high stability. Surface acoustic wave (hereinafter also referred to as “SAW”) oscillators, each of which is composed of a SAW resonator as a piezoelectric resonator element using a surface acoustic wave and a semiconductor circuit element (hereinafter referred to as “an IC chip”) having an oscillating circuit for driving the SAW resonator as an integrated circuit, are widely used as the oscillators suitable to have a high-frequency property, and transmitters and so on equipped with the SAW oscillators are also used widely. Further, in accordance with a requirement of downsizing and low-profiling to communication devices such as cellular phones, in order for achieving further downsizing, an SAW oscillator having the SAW resonator and the IC chip housed in the same package is disclosed in, for example, JP-A-9-162691 (Document 1).
The SAW oscillator of the Document 1 is provided with a package composed of a package base and a lid member, an IC chip (LSI) having electrode pads (external connection electrodes) formed on a principal surface, and an SAW resonator (an SAW chip) having IDT electrodes and external connection terminals (input/output electrodes) connected to the IDT electrodes formed on a surface of a piezoelectric substrate. The IC chip is fixed to a concave bottom portion of a recess section of the package base. The SAW resonator is bonded on the IC chip via a plurality of bumps, and is held so as to form a space between the IC chip and a surface to which the SAW of the SAW resonator is propagated. Further, electrode pads of the IC chip and the external connection terminals of the SAW resonator are electrically connected to each other via the bumps. Further, since the package is formed by bonding the lid member on an opening section in the upper surface of the base, the IC chip and the SAW resonator are airtightly encapsulated inside the package.
Incidentally, in general, in the case in which the SAW oscillator is used for a transmitter, it is necessary that when connecting the output of the SAW oscillator and an antenna to each other, an impedance matching circuit is inserted therebetween to form a filter for reducing high-frequency loss and unnecessary radiation. Further, it is possible to obtain a variation range of the frequency by varying a load capacitance connected to the oscillation circuit for performing frequency control by varying the frequency of the SAW oscillator or realizing frequency modulation in a voltage controlled SAW oscillator, and it is known that an inductive element such as an extended coil is inserted between the SAW resonator and the oscillation circuit in order for obtaining a sufficient variation range.
As the circuit parameters such as resistances, capacitances, or inductances required to the circuit components such as resistor elements, capacitor elements, or inductive elements used in such cases, large values, which are difficult to form by integrating them in an IC chip using the CMOS process, are required. Therefore, since it is necessary to use the resistor elements, the capacitor elements, or the inductive elements formed as relatively large chip components, there is caused a problem that increase in mounting space is resulted, and thus downsizing of the piezoelectric oscillator or the transmitter using the piezoelectric oscillator becomes difficult.
Further, in the case in which downsizing of the piezoelectric oscillator or the transmitter using the piezoelectric oscillator is given greater importance, and the matching circuit is not incorporated therein, the matching circuit needs to be provided to the mounting circuit board of the counter part on which the piezoelectric oscillator or the transmitter using the piezoelectric oscillator is mounted, and there is caused a problem that the advantage of downsizing of the entire communication device is reduced by half.